Peachey Conservation

January 18, 2009February 29, 2016

The Testing of Steel for Leather Paring Knives

[Update 29 Feb 2016: Starrett now tells me their red stripe blades are M2]

As the result of my own experience, feedback from some of my colleagues, and the results of scientific testing, I’ve become convinced that A2 cryro and machine hacksaw blades (M2 or M3 steel) are the best steel types for bookbinding knives. By best, I mean they offer what I consider an optimum balance of edge retention, initial sharpness, ease of resharpening and price for a leather paring knife.

Four leather paring knives were tested by Cutlery and Allied Trades Research Association (CARTA), located in Sheffield, England. The knives were tested for Edge Angle, Hardness, Initial Cutting Performance and Cutting Edge Retention. The steels tested were O1, A2, Machine hacksaw blade, and T15. All the steels rated very good to excellent, overall. O1 is a popular, standard knife steel, which I make many styles of knives out of, and it works very well on regular, vegetable tanned goat. Machinery’s Handbook recommends it when extreme sharpness is required. A2 is a newer, high tech steel gaining favor among woodworkers, since it holds an edge longer than O1. Most large woodworker blade suppliers make both O1 and A2 versions of plane blades, so there is some personal preference involved- do you like to spend a slightly longer time sharpening (A2) or sharpen more often (O1). Some type of overall time analysis might be conducted, but I can’t imagine it would be very informative given the wide range of unique variables the affect knives in use and when resharpening. Some bookbinders also use knives made from D2- but I find the high chromium content and coarse carbide structure (up to 50 microns!) make it cut poorly, more like stainless steel than a tool steel. Fully hardened machine hacksaw blades are traditional metal (starting mid. 20th C.?) for bookbinders to make paring knives from, I assume since it can be purchased already hardened and shaped by stock reduction. Starrett told me their “Red Stripe” blades are made from M3 steel, and I have read the English Eclipse ones are made from M2. T15 is a super expensive, very high tech steel that outperformed all the other blades, but the inital cost to me, and the number of grinding belts it ate up and time it took when shaping would result in a $750 knife, and I doubt anyone would purchase a $750 knife. And you would almost require a set of diamond stones to resharpen it.

I shaped and sharpened all of these knives by hand to a 13 degree angle. I suspect it is one of the first times that these types of steel were tested at such low angles– at typical woodworking blade is usually 25+ degrees. The blades were shaped on a 2 x 72″ Cootie Belt Grinder, progressing through US grits of 36, 100, 220, followed by hand sharpening on 3M microfinishing films of 40, 15, 5 microns, then stropped on vegetable tanned horsebutt with a .5 micron chromium oxide and finished by stropping on the flesh side of undressed vegetable tanned calfskin. The sharpness was tested on a pack of test cards containing 5% silica for 60 cutting cycles, 50N test load and 50mm/sec. test speed. CATRA has invented and sells many machines for sharpening and knife testing.

1. BEVEL ANGLE

Although I was attempting a 13 degree angle, the edge angled measured between 14-16 degrees for all of the knives when measured with a laser goniometer. I think this is the result of not being able to hold the knife angle consistently enough when sharpening and the result of stropping. There also was a general tendency for the angles to be slightly more acute (.5- 1.5 degrees less) at the sides of the cutting edge as compared with the middle. This is most likely the result of natural hand motion when sharpening, since I usually sharpen parallel to the cutting edge. I suspect if I was in the habit of sharpening perpendicular to the cutting edge, the edge angle would be even more obtuse.

2. HARDNESS

Average from three testing points near the cutting edge in Rockwell C scale.

A2 – 62

Hacksaw (M3) – 64

O1 – 64

T15 – 65

3. INITIAL CUTTING PERFORMANCE (mm)

This is how “sharp” the knife is; how far it penetrated into the cards during the first three cutting strokes.

Tested in accordance with BS EN ISO 8442-5: 2004, Part 5 (Clause 3.4- Cutting Performance)

A2 – 107

Hacksaw (M3) – 107

O1 – 98

T15 – 116

4. CUTTING EDGE RETENTION (mm)

This is how long the edge lasted– ie. the ability for the edge to resist wear. This is the cumulative depth of 60 cycles of cutting the test pack.

A2 – 522

Hacksaw (M3) – 586

O1 – 395

T15 – 921

CHART OF CUTTING EDGE RETENTION RESULTS

A2 is light blue

Hacksaw is green

O1 is dark blue

T15 is red

CONCLUSIONS. Initially, A2 has a slightly slower rate of dulling, which may be an advantage, but later in the test the Hacksaw slightly surpasses it. The O1 seems to have a very constant, predictable rate of dulling- the graph is very smooth. The T15 is incredible- even at the end it was still cutting quite deep, and each cut it still quite deep. Since O1 is about 400, and A2 is about 600, does this mean A2 is 20% better? Given all the complex variables in use, it is hard to accurately observe. As with most scientific testing, a primary conclusion is the need for more testing. I would like to compare bevel angles at 2.5 degree increments, add a number of different types of steel, like some of the M and S tool steel classes, maybe some of the new high carbon stainless steels and instead of testing with a sample card containing silica, test actual tanned and tawed leather. Also the pressure on the blade may be much more than is necessary (or possible) to pare leather, and the sawing motion of the testing machine is different than a more static blade motion that bookbinders use.

knife-shart1

January 12, 2009January 28, 2013

The Shift From Mechanical to Adhesive and Beyond

19th-c

Clark, Adam. Christian Theology. New York: T. Mason and G. Lane, 1837.

I always enjoy examining these 19th C. (or early 20th C.) book repairs where the board is sewn to the spine. This example is fairly crude, but some can actually function fairly well. This book is in my collection– I will preserve it as evidence of the history of book repair. We might find this repair laughable, but it is fairly easily reversed, there is no glue to remove and it kept the boards from getting lost. When the holes in the spine are staggered through a number of signatures, these repairs hold up fairly well, and if the paper drapes well and the spine is fairly flat, as in this example, all of the text is easily readable.

sewn-board

sewn-board-2

This example is missing the title page and first 14 pages, but I think it is some kind of Catholic devotional book. It is bound in typical early to mid 19th C. style and is quite small– 84 x 57 x 34 mm. Of course, I am not advocating this as a type of repair a conservator would do today, but to me it represents a 19th C. common sense approach to the most common failure in book structure– detached boards. This type of repair, fairly common in the US, might have served as impetus for joint tacketing or a literal “sewn-boards” binding. The upper board and lower board are sewn differently, the lower board like the previous example, but in the case of the upper board, the stitch runs into the edge of the board, which results in a decent opening. The brown thread which matches the calf covering is doubled like sewing thread is. Could this this have been done by a woman, and the previous “heavy duty” example done by a man?

board-edge-drilling

I have hypothesized elsewhere that there might be some kind of connection between early board attachments such as in the Book or Armagh, Romanesque lacing paths, and board slotting. The spine edge of a book board is a very tempting entry point in establishing mechanical attachment. The strength, and relative noninvasiveness of board edge attachments make it an appealing treatment option, alleviating the need for disruptive lifting of covering materials. I have been experimenting with a new jig, pictured above, which holds a foredom drill at a precise angle, and has a depth stop, to accurately drill with wire gage drill bits, in order to drill a hole exactly the size of the thread used to reattach the board.

Advertisement from Science and Mechanics, Vol. XVII, No. 6, 1946, p. 38.

By the mid 20th C., detached boards and other types of damage are more commonly fixed by tapes and adhesives, as the advertisement above suggests. Unfortunately, I think I have seen this used on books. It ends up looking like a thick, completely inflexible amber mass of goop. I think this glue is the kind I used to use as a kid when assembling plastic or balsa wood models. The cap of this tube is unusual- it looks like a twisted loop of wire, perhaps used to pierce the top when opening? Often the spine edge of the detached board is glued to the flyleaf to “fix” a detached board.

By the early 21st C.,in the general public, most ideas of repairing an object mechanically are gone, and most ideas of repairing an object by using adhesives are gone. In fact, the idea of repair is almost gone. We simply buy a new one, unless the book has some kind of exceptional value.

The idea of a world where nothing is worn, nothing is fixed and everything is new frightens me. How would one conserve an ebook reader? I’m sure books will exist for a very long time, but more as symbolic representations of learning and knowledge, not primarily as a source for accessing a text. This is why these primitive, vernacular repairs are so important for understanding a previous culture’s relationship to the books they used, treasured, repaired and read.

January 5, 2009January 28, 2013

Turkish Knife and Saw Handles

This is a small serrated folding knife. I wasn’t able to figure out what it was used for–the serrations are very fine. As you can see in the photo, the sides are ground slightly and taper towards the cutting edge. The back of the blade is about .020″, and it tapers towards the cutting edge which is a very thin .010-.007″. The shape is similar to a modern pruning saw which also has a pistol type handle. It was made in Bursa, Turkey, which is the center for metal working– like Sheffield in England, or Solingen in Germany.

I find the handle the most interesting feature since it fits comfortably into the heel of the hand. It cuts, Eastern style saw, on the pull stroke. It cost $4.00 and was quickly made- note the crude ferrule and pivot pin, however the complex curves on the handle must have taken some time. But it feels surprisingly solid.

This illustration is from a Ward and Payne Ltd., Sheffield catalog, circa 1910’s. This is called a Turkish Saw (aka. Monkey saw) According to Salaman’s Dictionary of woodworking tools, they are common in Greece, Crete and Turkey and are used as a dovetail or small tenon saw. Again, it cuts eastern style on the pull stroke, so the blade can be made thinner. And like the knife above, the handle looks very comfortable, since it extends near to the wrist at the very end.